Abstract C89: The small molecule inhibitor 4SC-202 controls aberrant HH signaling in cancer

Introduction: 4SC-202, a clinical stage inhibitor of LSD1 and HDAC1, 2 and 3 was investigated to identify its unique mechanism to target cancer cells by controlling aberrant Hedgehog signaling. Experiments: 4SC-202 is an oral available epigenetic modulator exhibiting a combined inhibition of the lysine specific demethylase LSD1 (KDM1A) and histone deacetylases HDAC1, 2 and 3. 4SC-2029s impact on Hedgehog signaling activity was tested in a SMO-dependent setting and in a SMO-independent setting. Therefore, Hedgehog signaling in DAOY cells was either activated by addition of sHH or Smoothened agonist or by stable depletion of SUFU for instrinsic, SMO-independent signaling. Pathway activity was determined by the expression of the effector protein GLI and primary target genes. SMO-independent Hedgehog signaling can be driven as well by growth factors like TGF-s as demonstrated for the pancreatic cancer cell line PANC1. Therefore, 4SC-2029s impact on spheroid formation and protein expression was tested in PANC1 cells. Results: Compared to HDAC inhibitors like Vorinostat, LSD1 inhibitors like OGL-002 and Hedgehog inhibitors targeting SMO like Vismodegib, 4SC-202 was able to inhibit canonical as well as non-canonical GLI-driven Hedgehog signaling. Additionally, 4SC-202 was able to prevent spheroid formation of pancreatic cancer cells and inhibit TGF-s driven signaling in PANC1 cells. Conclusion: Aberrant activity of the Hedgehog signaling pathway has been implicated in the development, progression and relapse of different cancer entities. Especially the interaction of tumor cells and the microenvironment is driven by SMO-independent Hedgehog signals and therefore Hedgehog inhibitors targeting SMO like Vismodegib were not able to demonstrate clinical benefit in SMO-independent Hedgehog driven cancer types like PDAC. The unique feature of 4SC-202 to control both SMO-dependent and SMO-independent HH signaling provides the opportunity to demonstrate activity in Hedgehog driven entities in further clinical investigations. 4SC-202 was safe and well tolerated in a phase I clinical trial (TOPAS) in patients with advanced hematological diseases. With a disease control rate of 83%, one partial responder treated for 8 months and one complete responder treated for 28 months, patients benefited from 4SC-202 treatment and hints of activity could be demonstrated. Citation Format: Hella Kohlhof, Wolfgang Gruber, Daniel Vitt, Fritz Aberger, Tanja Prenzel. The small molecule inhibitor 4SC-202 controls aberrant HH signaling in cancer. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr C89.